Lithography methods have been frequently used for the production of fine features in various kinds of electronic devices, such as semiconductor devices. In recent years, as the device features are further miniaturized, miniaturized resist patterns with increased aspect ratio in lithography processes have been also desired. For attaining the formation of such a fine pattern, a first step is to improve a lithography device and to develop a corresponding resist. Common factors to consider for developing the lithography device include shortening of wavelengths of light sources such as F2 excimer laser, EUV (extreme UV light), electron beam, X-ray, soft X-ray and the like, and increases in numerical aperture (NA) of lens.
On the other hand, shortening the wavelengths of the light sources requires a new and expensive aligner (lithography device). In addition, a problem arises in that a focal depth width is reduced even if the resolution property is improved because a trade-off lies between the resolution and the focal depth width when the NA of lens is increased.
Accordingly, as a lithography technique for solving such problems, liquid immersion lithography (hereinafter, may be also referred to as “liquid immersion exposure”) was proposed (see Nonpatent Document 1). In the liquid immersion exposure, a liquid (liquid immersion medium) having a refractive index higher than that of air is placed between an objective lens of the lithography device and a resist film (or resist protective film), and then the exposure (immersion exposure) is carried out. Regarding such liquid immersion exposure, a high resolution can be reportedly achieved even when a light source with the same exposure wavelength is used, similarly to the case in which a light source with a shorter wavelength and in which a high NA lens is used, and also a decrease in the focal depth width is not reportedly resulted. Additionally, the liquid immersion exposure can be carried out using a preexisting lithography device. Therefore, the liquid immersion exposure is expected to be capable of realizing formation of resist patterns with a high resolution and also with favorable focal depth width at low cost. Thus, it has drawn great attention in manufacturing semiconductor elements which require a large amount of investment in equipment, owing to great effects exerted on semiconductor industry in terms of cost, as well as lithography characteristics such as resolution.
The liquid immersion exposure is efficacious in forming any pattern configuration, and further it is reportedly possible to use it in combination with a super-resolution technique currently being investigated such as a phase shift method, a modified illumination method or the like. At present, techniques in which an ArF excimer laser is employed as a light source have been mainly studied actively as the liquid immersion exposure technique. In addition, water has been predominantly investigated currently as the liquid immersion medium.
In liquid immersion exposure, for example, water is placed as a liquid immersion medium between an objective lens of the lithography device and a resist film (or resist protective film); therefore, there is an envisaged problem that water runs around the edge portion (outer edge) or the back face of the substrate. In order to prevent such running of water, it is efficacious to hydrophobilize the substrate.
Conventionally, as a method for hydrophobilizing a substrate, a vapor treatment by means of hexamethyldisilazane (HMDS) with bubbling of nitrogen has been extensively adopted (see Patent Document 1). Also, for the purpose of further increasing hydrophobicity, a method carried out using a silylating agent having an alkyl group or alkenyl group substituted with fluorine in place of HMDS was proposed (see Patent Document 2).
However, the vapor treatment with a silylating agent as in Patent Documents 1 and 2 is hardly recognized as being a simple method since it necessitates heating, bubbling of nitrogen or the like. In addition, the center section of a substrate is often provided with an inorganic bottom antireflective coating (inorganic BARC) or an organic bottom antireflective coating (organic BARC), and hydrophobilization of such a section is believed to be unnecessary. In this regard, the vapor treatment with a silylating agent is not efficacious since such a section on which hydrophobilization is not required is also subjected necessarily to the treatment.
Furthermore, a problem of pattern collapse, generally referred to, is marked as further miniaturized resist patterns with increased aspect ratio in lithography processes are provided. The pattern collapse means an event that occurs in forming a large number of resin patterns in parallel on a substrate, in which adjacent resin patterns get close such that they lean to each other, and the resin patterns may be broken off or detached from the basal part in some cases. Occurrence of the pattern collapse leads to failure in obtaining desired products, thereby resulting in deterioration of the yield and decrease in reliability of the products.
Moreover, the problem of pattern collapse recently arises not only on resin patterns but also on etched patterns.
The pattern collapse has been known to be caused in a washing treatment following the pattern formation when the washing liquid dries, owing to the surface tension of the washing liquid. In other words, when the washing liquid is removed off in the drying step, a stress resulting from the surface tension of the washing liquid acts between the patterns, and thus the pattern collapse occurs.
Therefore, many efforts have been made hitherto for preventing pattern collapse by adding a substance for decreasing the surface tension to the washing liquid. For example, washing liquids containing isopropyl alcohol, washing liquids containing a fluorochemical surfactant, and the like were proposed (see Patent Document 3 and 4).
However, only the ingenuity of the washing liquid as proposed in Patent Documents 3 and 4 has involved the problem of insufficiently achieved prevention of pattern collapse.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. S60-25231
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2007-19465
Patent Document 3: Japanese Unexamined Patent Application, Publication No. H6-163391
Patent Document 4: Japanese Unexamined Patent Application, Publication No. H7-142349
Nonpatent Document 1: Proceedings of SPIE, Vol. 5754, pp. 119-128 (2005)